Low-Cost Maximum Efficiency Tracking Method For Wireless Power Transfer Systems

This paper presents a novel maximum efficiency point (MEP) tracking method for wireless power transfer (WPT) systems. It is proved that at the MEP for a typical system containing a boost converter on the receiving end, the derivative dD/dV(in) (V-in being the inverter's dc input and D being the duty cycle of the converter) is equal to or smaller than a constant beta that is determined by system parameters. By tuning Vin and comparing dD/dVin with beta, the MEP can be tracked without a power or current sensor, hence reducing the tracking cost. A WPT system is demonstrated experimentally to verify the method. When the diameters of and the vertical distance between the transmitting and receiving coils are 4.3 and 2.35 cm, respectively, without horizontal misalignment, high efficiency is maintained even when the load ranges from 5 to 100 Omega, and the efficiency improvement reaches 41.2% when compared to the measured efficiencies without the proposed method. The differences between the maximum efficiencies tracked by the proposed method and the manually searched maximum values are at most 1.8%. Extension of the proposed method to WPT systems employing other popular forms of inverter, dc/dc converter, and coil topology is also presented.